The invention relates to a device for automatic withdrawal of a gauged volume of pulverulent solid, liquid or gaseous materials present in a withdrawal zone in which the prevailing pressure is greater than, equal to or less than atmospheric pressure, and for conditioning of these withdrawn materials for the purpose of analysis thereof.
For a long time, industries, such as, for example, the chemical industry, the metallurgical industry, the agri-foodstuffs industry, etc., have used raw materials which they convert to intermediate products or to finished products which man exploits, uses or consumes for his survival, comfort, etc.
The processes of transformation of raw materials to intermediate products or finished products which are pulverulent, liquid or gaseous in form pass through successive stages of working-up, and these require that controls should be carried out, such as controls of, for example, particle size, chemical composition, physical properties, reactivity, purity, and the like.
To perform suitable controls, the expert has to carry out the withdrawal of homogeneous, representative and repeated samples of the products obtained during the conversion of the raw materials, so that they can be examined continuously or discontinuously and that the deficiencies and/or imperfections can be detected and corrected by a rapid intervention, for example, in the conversion process.
For a long time, the technology of withdrawing samples of materials for analysis during industrial processes has consisted of manual equipment for taking samples at places and times which are insufficiently precise for the samples to be beyond dispute for the expert, that is to say, to be representative of a given state at an identified place and a precise moment. It is the case, for example, that in hydrometallurgy, to determine and follow the rate of settling, in a large sized settler (diameter: twenty meters; height: five meters), of a solid phase in an aqueous suspension resulting from the attack of an ore, sampling was carried out by lowering a closed cylindrical measure to a depth which is fixed but only approximate, since it is observed by the unwinding of a length of cable, and then opening and closing the measure again, by manual operation, when it has reached the presumptive withdrawal zone, before raising it again. However, the sampling point of the suspension is never exactly the same from one withdrawal operation to the next, so that the analysis of each withdrawal gives approximate information which is, however, insufficiently objective and representative of the state of settling of the suspension.
Since then, improved devices for withdrawing samples have been proposed. Such devices are capable of carrying out these withdrawals in a precise and methodical manner, without human intervention, in order that each sample withdrawn should be fully representative of the material to be controlled.
An example of an improved device for automatic sample withdrawal is described in Frensh Pat. No. 2,258,108. This device incorporates a cylindrical horizontal probe in which there is provided a longitudinal recess of specified capacity and of shape suitable for the nature of the material to be sampled. Driving means drive the probe in longitudinal repriprocating motion, and guiding means direct the recess in the probe upwards in the filling position, when the probe is inside the withdrawal zone, and downwards in a discharge position in a receptor zone when it has been removed from the withdrawal zone. The probe is equipped with a shutter consisting of a cylindrical coaxial sleeve, provided with an opening of dimensions at least equal to those of the recess formed in the probe. This shutter is driven in longitudinal reciprocating motion by driving means and in rotatory motion by other guiding means designed to rotate the sleeve relative to the probe. The recess in the probe coincides with the opening in the sleeve at the times when the probe is in position for withdrawal and for discharge of the sample, and the recess is masked during the intermediate phases of the probe.
This device, however, has certain disadvantages. For example, it does not prevent leakage between the zones for withdrawal and for discharge of the sample. Nor does it protect the physical characteristics of the sample between withdrawal and discharge from infiltration of particles foreign to the sample. For this reason, a first improvement of this device was proposed and described in Patent FR A No. 2,271,559. This improved device incorporates a fixed, no longer movable, coaxial cylindrical shutter (sleeve) sealed integrally to the separation partition between the withdrawal and discharge zones, the abovementioned opening in the shutter being located in the discharge zone facing downwards. The withdrawal probe moves inside the fixed cylindrical shutter, its translational and rotational movements being guided by a continuous groove located on the shutter and a radial pin integral with the probe projecting into the groove.
The device described in Patent FR A No. 2,258,108 also has another disadvantage, however which appears during operation of the probe. When the probe is removed from the withdrawal zone, it wedges a particle of sample material between the rear edge of its recess and the end of the shutter which opens into the withdrawal zone. To limit this disadvantage, a second improvement of the abovementioned device was claimed in Patent FR A No. 2,288,307. This second improvement consists in providing the front end of the probe, situated forward of the recess, with a flat or gap of depth greater than the particle size of the material to be sampled.
As a result of this, at the end of the retraction movement of the probe, this flat (or gap) forms with the inner wall of the shutter a space which enables the particles of material to be released without them being wedged or disrupted.
This device and its improvements, which offer undeniable advantages with respect to the prior art in the field of sampling of granular materials, nevertheless possess other disadvantages than those already mentioned, which can be of major importance and especially troublesome for their industrial use. A first disadvantage is, for example, the definite lack of imperviousness to leakage between the withdrawal and discharge zones and between the withdrawal probe, and coaxial cylindrical shutter (whether fixed or otherwise) and the guiding means. Another disadvantage resides in the fact that the shape of the probe in the recess portion is self-destructive for the gaskets which would be installed in this device in place of the self-luricating materials. Finally, a further disadvantage, which results from those mentioned above, relates to the impossibility with this device of carrying out withdrawals of materials in the liquid phase, such as a solution or suspension, and in gaseous phase, or of carrying out withdrawals of materials whether in the solid, liquid or gaseous state when the withdrawal zone is at a pressure greater or less than atmospheric pressure.
As a result, and by virtue of the above-mentioned disadvantages, the Applicant, continuing his investigations, has discovered and perfected a device for automatic withdrawal, and also for conditioning, of a measured volume of pulverulent solid, liquid or gaseous materials, for the purposes of analysis thereof, in a withdrawal zone in which there prevails a pressure greater than, equal to or less than atmospheric pressure.